Offshore hydrocarbon exploitation leads to the use of various treatment methods on oil platforms. However, when the sea is too deep, it is not possible to use stationary platforms, and floating platforms, often called FPSO (Floating Production Storage and Off-loading), are used. These floating platforms are subject to the movements of the sea, which they transmit to the equipment they bear. Among these, the columns, whether distillation or absorber columns, are among the most sensitive to movement. In fact, the effectiveness of this equipment depends on the quality of the contact between the descending liquid and the vapor that rises in the columns.
The most traditional method for establishing good contact between the liquid and vapor consists of forcing the gas to pass through ports formed in a tray on which the liquid flows. However, in such tray columns, the quality of the contact between the liquid and vapor depends on the horizontally of the trays; any angle relative to the horizontal, even a small one, can lead to dry a part of the tray from liquid, which then no longer ensures contact between the liquid and vapor. For that reason, operators of plants on floating platforms prefer random or structured packing over trays. Document FR 2777533 describes a floating maritime structure having a structured packing with a particular geometry designed to reduce the impact of the marine oscillations on the operation of the structure.
Random packing consists of metal or ceramic pieces that are positioned so as to fill the entire cross-section of the column, in a disordered manner. The complex shape ensures good contact between the liquid and the vapor. Structured packing consists of plates shaped and arranged together so as to ensure the passage of the gas and liquid with good contact.
FIG. 1 shows a traditional column arrangement equipped with packing. The configuration is similar for disordered packing and structured packing. The column here comprises two packing beds A and B. They are sprayed with liquid using distributors C and D that ensure the distribution thereof on the entire cross-section of the column. A collector E collects the liquid from the bed A; the liquid is then distributed by the distributor D on the bed B. The proper operation of the packing assumes that the liquid is regularly distributed over the entire cross-section of the column so as to avoid dry areas, which would cause part of the rising vapor not to be in contact with the liquid.
In traditional liquid distributors, the liquid coming from the top of the column arrives in a chute, the bottom of which is pierced with holes. Each of these holes is across from a secondary chute that it feeds with liquid. The secondary chutes, the bottoms of which are in turn pierced with distribution holes, ensure uniform spraying of the cross-section of the column.
Furthermore, in traditional liquid distributors, the chutes are open at the apex and the liquid level established inside is also subject to the movements of the FPSO. As a result, depending on the incline, the distribution holes are covered by a higher or lower liquid level. Since the flow rate through each hole depends on the liquid height submerging it, the flow rates are therefore not identical, which leads to irregular spraying of the cross-section of the column. Certain distribution ports may not be submerged in the liquid, which leads to dry areas in the packing. The liquid/vapor contact quality is therefore affected.
Document US 2008/0271983 proposes to modify the liquid distributor so as to ensure a regular distribution of the liquid over the entire cross-section of the column, irrespective of the incline. An illustration thereof is provided in FIG. 2, taken from that document.
The liquid is distributed on the cross-section of the column using primary 32 and secondary 33 chutes which, unlike traditional distributors, are closed. Each primary chute 32 is supplied by a vertical tube 31. The chutes are pierced on the lower surface thereof with ports that ensure the distribution of the liquid, whereof the diameter is calculated such that the liquid level is established relatively high in the vertical tube 31. Thus, the pressure differences that may appear at the perpendicular to each of the ports due to the incline of the column become negligible faced with the hydrostatic height produced by the liquid level in the vertical tube 31. A uniform distribution of the liquid may thus be ensured over the entire cross-section of the column. These distributors are described as pressure distributors.
However, the main drawback of this device lies in the height of liquid that is necessary in the vertical tube 31. In fact, for the device to be effective, this height must be significantly greater than the height variations between the different parts of the chutes that result from the incline of the column. The height of the vertical tube 31 therefore commonly reaches 3 to 4 m.
Furthermore, when the column is inclined, the liquid tends, within the packing, to accumulate on the side toward which the column is tilted, until it may encounter the shell on which it flows without returning toward the inside of the packing. The uniformity of the liquid distribution obtained using the pressurized distributor is thus broken. In order to avoid this harmful effect, it is necessary to collect the liquid and redistribute it approximately every 4 to 5 m so as to eliminate the edge effects.
As a result of the above, the height of a column following the model of that described in document US 2008/0271983 is significantly greater than a standard column, with an equal flow rate. This results in bulk and weight constraints that are difficult to reconcile with the constraints of a tight environment, such as that of floating platforms. Consequently, there is a need to design a new unit for establishing contact between a gas and a liquid that is capable of operating effectively on a floating platform despite the movements thereof, and having smaller sizes than the units of the state of the art.